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To investigate how the concentration of sodium thiosulphate as it is diluted with water and then added to hydrochloric acid, affects the rate of reaction.

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Sodium thiosulphate investigation Aim: To investigate how the concentration of sodium thiosulphate as it is diluted with water and then added to hydrochloric acid, affects the rate of reaction. Prediction: I think that as I dilute the sodium thiosulphate with water and then add it to the hydrochloric acid, the time for the rate of reaction will increase. I have followed a special theory for this. The theory is the collision theory, which states, as you increase a substance there are more particles in it resulting in more collisions. This theory can also work vice versa because in this experiment we will be decreasing the concentration of sodium thiosulphate resulting in less collisions, therefore extending the time for the reaction to take place. In a low concentration, the particles will be few and widely spread. This means that the number of reactions will be limited because fewer particles will meet. At higher concentrations there are more particles and so they probability of them coming into contact with other particles is increased. But in this experiment we are swiftly decreasing the concentration of sodium thiosulphate. This theory is applied when the reaction is applied. ...read more.


I also made sure someone always stayed on top of the beaker to observe when the cross-disappeared. I always made sure that I never moved the beaker a lot because I didn't want any more collisions resulting in a faster rate of reaction. I always repeated my exercise 3 times, so I could get a more accurate mean average. I used the Internet a lot to research on rate of reaction, so I could extend my knowledge on this subject, giving better observations. Quantities used: Experiment no. Volume of sodium thiosulphate CM3 Volume of water used CM3 Volume of HCL used CM3 Total volume CM3 1. 35 00 05 40 2. 30 05 05 40 3. 25 10 05 40 4. 20 15 05 40 5. 15 20 05 40 6. 10 25 05 40 7. 05 30 05 40 Results: (on graph paper) Conclusions: From my graph I can see that most of my results were correct, although I did have an anomalous result. My results agree with my prediction because I predicted that the lower the concentration of sodium thiosulphate, and the higher the amount of water, the longer the reaction would take to occur. ...read more.


These were probably due to me rushing the measuring of each solution. We were set a certain time limit of one 50-minute lesson, to get each solution done at least twice so I might have rushed. Other reasons for these anomalous results could be that the eye could also have made mistakes in judging whether or not the cross-had actually completely disappeared. If the same person watching the reaction was working the timer, errors could occur in their co-ordination. Using a burette to measure. This would remove the measuring errors associated with measuring cylinders, as they are correct to 0.1 cm where measuring cylinders are only 0.4. Burettes are a far more accurate way of measuring the correct amounts. Use light sensors to detect when the cross is no longer visible. The experiment could be connected to a light sensor, and to a timer. These light sensors will detect when there is no light shining through the substance. This would automatically stop the timer and therefore make the experiment fairer and more accurate. Doing each solution on separate occasions and repeating them more than three times giving me a better average could have extended my investigation. But these choices were out of my control. Altogether I am quite pleased with my investigation and my results. ...read more.

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